In a receiver optical sub-assembly (ROSA), a photodiode chip packaged in a transistor outline (TO) can (or package) is typically used to detect optical signals received over an optical fiber. In a conventional TO can for receiving optical signal at a transmission rate of 10 Gbps (Giga bits per second) or higher, the photodiode chip is located at the center of the TO header. Such centering of the photodiode chip allows the active area of the photodiode chip to be co-axial to the optical fiber. However, limiting the location of the photodiode chip to the center of the TO can results in an inflexible configuration. In such at-the-center photodiode chip configuration, it may be difficult to place other components at locations that will reduce distance between them or to the leads for wire bonding, for example.
In addition, when the photodiode chip is co-axial with the optical fiber, relatively high return loss typically results due to reflection of the optical signal that interferes with the optical output of the optical fiber. The edge of the optical fiber is often slanted at an angle to reduce the reflection incident upon the optical fiber. However, such slanting of the edge typically results in low optical coupling efficiency, for example, due to resulting optical aberration when the chief ray of the optical signal is bent as it passes through the periphery of the lens.